Abstract

Background

Many viruses have evolved multiple strategies to prevent super infection of host cells
by more than one virion. This phenomenon, known as super infection exclusion, may
play an important role on virus evolution because it can affect the frequency of reassortment
and/or recombination. Newcastle disease virus (NDV), a negative sense single-stranded
RNA virus, is characterized by its continuous evolutionary dynamics and by a low frequency
of recombination events. However, the mechanisms that contribute to the low recombination
rates on NDV are still not completely understood.

Methods

In this study we assessed the ability of two NDV strains (LaSota and B1) to super
infect host cells in vitro. We generated a recombinant NDV strain LaSota expressing the red fluorescent protein
(RFP) and used it in co-infection assays with a related NDV strain B1 expressing the
green fluorescent protein (GFP). DF-1 cells were inoculated with both viruses at the
same time or at different intervals between primary infection and super infection.

Results

When both viruses were inoculated at the same time point, a 27% co-infection rate
was observed, whereas when they were inoculated at different time points the super
infection rates decreased to levels as low as 1.4%.

Conclusions

These results indicate that although different NDV strains can co-infect host cells
in vitro, the super infection rates are low, specially as the time between the primary infection
and super infection increases. These results confirm the occurrence of super infection
exclusion between different strains of NDV.